The present invention relates &o a method of and an apparatus for recording an image, and more particularly to a method of and an apparatus for recording an image while effectively processing image signals for increased sharpness or the like in an image scanning recording system such as a scanner for making a printing plate, a facsimile transmitter/receiver, or the like.
Image scanning recording systems are widely used in the printing and platemaking industries for electrically processing image information of originals or subjects to produce original film plates with a view to simplifying the entire process and improving the quality of printed images.
The image scanning reproducing systems are basically constructed of an image reading apparatus and an image recording apparatus. In the image reading apparatus, image information of an original or subject which is fed in an auxiliary scanning direction is scanned in a main scanning direction substantially normal to the auxiliary scanning direction, and the scanned image information is converted to an electric signal. Then, the photoelectrically converted image information is processed in the image recording apparatus for signal processing according to platemaking conditions. Thereafter, the processed image signal is converted back to a light signal which is applied to and recorded on an image recording medium such as a photographic film. The image recording medium with the image recorded thereon is developed by an image developing device and will be used as a film plate for printing.
Where an original image is a continuous-gradation image such as a photographic image, the image signal produced from the image is subjected to a sharpness enhancing process for sharpening the edge or contour of the image. The sharpness enhancing process is effected as shown in FIG. 1 of the accompanying drawings, for example. First, an image signal S is picked up from a desired pixel in an original image, and (n .times. n) image signals are picked up from corresponding pixels disposed around the pixel from which the image signal S has been produced. Then, the (n .times. n) image signals are added and averaged to generate an unsharp signal U. The difference signal between the image signal S and the unsharp signal U is calculated, and then multiplied by a prescribed coefficient (sharpness parameter) K. The product is added to the image signal S. As a result, an image signal S* which is subjected to the sharpness enhancing process is given according to the following equation: EQU S*=S+K.multidot.(S-U) (1)
After a continuous-gradation image such as a photographic image has been enhanced in sharpness, the image is converted to a halftone dot image. More specifically, the image signals are converted to on-off signals based on a predetermined halftone dot signal, and a halftone dot image composed of halftone dots of desired sizes is formed on a recording medium based on the on-off signals.
When the size of halftone dots used in the halftone dot image forming process is increased, e.g., coarse half-tone dots (the number of halftone lines: 64 to 85 lines/inch) are used for newspaper printing or the like, the size of an image mask which is composed of the (n .times. n) pixels selected to produce the unsharp signal U in the sharpness enhancing process becomes small relatively to the above halftone dot size. In this case, the degree to which the image edge is sharpened by the sharpness enhancing process becomes smaller, i.e., the desired sharpness of the image cannot sufficiently be achieved.
Therefore, for increasing the size of halftone dots, it is necessary to increase in advance the number of pixels used to produce an unsharp signal U for effecting a sharpness enhancing process. If the number of such pixels is increased, however, the storage capacity of a memory required for temporarily storing image signals which will be used in the sharpness enhancing process must also be increased.